A search for broad infrared recombination lines in NGC 1068

We report infrared spectroscopy of the prototypical Seyfert 2 galaxy NGC 10 68, aiming at detection of broad components of hydrogen recombination lines that originate in the obscured broad-line region. Using the Short Waveleng th Spectrometer on board the Infrared Space Observatory, we have observed f or the first time the regions of B beta 2.626 mu m and Pf alpha 7.460 mu m, and present improved data for B alpha 4.052 mu m No significant broad comp onents are detected, implying an equivalent visual extinction to the broad- line region of at least 50 mag and an obscuring column density of at least 10(23) cm(-2). While consistent with a highly obscured broad-line region, a s required by the classical unified scenario, these limits are not yet sign ificant enough to discriminate strongly between different torus models or t o constrain properties of the gas causing the very large X-ray obscuration. We discuss the systematic limitations of infrared broad-line region search es and suggest that B alpha may often be the most favorable transition for future searches.